The present invention relates to a method and apparatus for controlling the power to be delivered by a mixture-compressing internal combustion engine and, more particularly, to a method and apparatus in which power is adjusted by a setting element during normal operation of the engine by matching fuel injection quantity to induced air mass flow corresponding to a current load demand and the setting element is held in a constant opening position in the event of a functional fault thereof.
U.S. Pat. No. 4,779,597 discloses a method which provides for the throttle butterfly to be no longer actuated when it is found that there is an impairment of the function of this throttle butterfly and for the induced air flow to be guided via a by-pass conduit bypassing the throttle butterfly. The magnitude of the induced air mass flow passing this by-pass conduit, and therefore also the power of the internal combustion engine, being controlled by a valve device arranged in the by-pass conduit. It is, in turn, possible to trigger this valve device by way of an electronic control unit as a function, among other things, of a load demand signal (accelerator pedal position). This known method has the disadvantage that a separate by-pass conduit is required and that eddying of the induced air occurs where it branches from and opens into the induction conduit when no functional impairment of the main throttle butterfly is present. This eddying leads to a reduction in the volumetric efficiency which is of particular disadvantage at full load, i.e. with the main throttle butterfly open to the maximum extent, because it is precisely in this operating condition that a maximum volumetric efficiency is the precondition for a maximum power of the internal combustion engine. In addition, the components necessary for carrying out the known method (by-pass conduit, additional valve element and additional actuator) take up a relatively large installation space.
An object of the present invention is to provide a method such that, in the case of an impairment of the function of the setting element for controlling the induced air mass flow, control of the internal combustion engine power to be delivered still remains possible (emergency driving function) but, at the same time, no reduction in the volumetric efficiency of the internal combustion engine is to be expected in normal operation.
The foregoing object has been achieved in accordance with the invention by a method and apparatus in which, during existence of the functional fault, internal combustion engine power is adjusted to a value corresponding to the current load demand (.beta.) exclusively by one or more of interventions in mixture composition, interventions in ignition timing, and controlled interruption of the fuel delivery to at least one cylinder so as to provide cylinder shut-down.
With the method and apparatus according to the present invention, an additional by-pass conduit is unnecessary because the power to be delivered by the internal combustion engine is controlled exclusively by interventions in the mixture composition and/or by interventions in the ignition and/or by specific cylinder shut-down when there is an impairment of the function of the setting element controlling the induced air mass flow. Consequently, no eddying of the induced air flow can occur at the positions where such a by-pass conduit branches from the induction conduit or at the positions where it opens into the induction conduit so that, in normal operation of the internal combustion engine, a maximum volumetric efficiency is ensured, particularly at full load, i.e. with the induction conduit freed to its maximum extent. Furthermore, no additional installation space is demanded by a by-pass conduit and by a valve device, with associated actuator, controlling its cross-section.
If, according to the present invention, the setting element is driven by spring force into a specified opening position in the case of a functional fault, emergency driving operation is then also possible if the functional fault occurs at a time when the setting element happens to be in the closed position such as during idling of the internal combustion engine. In this situation, a larger air mass flow than the air mass flow provided in normal operation when idling is specified is again induced because the throttle butterfly is necessarily driven into a specified opening position so that, due to the measures according to the invention, control of the power to be delivered by the internal combustion engine remains possible over a wide range.